Bifocal eyeglass lens



June 5, 1923.

w. F. FIS HER BIFOCAL EYEGLASS LENS Original Filed May 12, 1920 2sheets-sheet I N VEN TOR. ILL 1AM F F7sHER.

A TTORNY8 June 5, 1923.

W. F. FISHER BIFOCAL EYEGLASS LENS Original Filed May 12, 1920 2Sheets-Sheet 2 INvE/VTORY WILLIAM F.' l /sHER:

A TORNE Y6? Patented June 5, 1923.

UNITED STATES PATENT orrics.

WILLIAM F. FISHER, OF MINNEAPOLIS, MINNESOTA.

IBIFOGAL EYEGLASS LENS.

Original application filed May 12, 1920, Serial No. 380,729. Divided andthis application filed April 23,-

p 1923. Serial No. 634,136.

T 0 all whom it may concern:

Be it known that'I, \VILLIAM F. FISHER, a citizen of the United States,residing at Minneapolis, in the county of Hennepin and State ofMinnesota, have invented certain new and useful Improvements in BifocalEyeglass Lenses, of which the following is a specification.

My invention relates to bifocal eye-glass lenses. An object is toprovide a one-piece bifocal lens for myopic corrections in which thedistance portion is ground in the reading portion, the segment which isthus ground out being at the upper portion of the finished lens toconstitute the distance portion. Myopic corrections require minus lenseswhich are thickest at the outer edge. hen lenses' of this character aremade with the segment on the bottom portion, there is a large amount .ofprism to over-, come in the reading portion of the lens, which has a.tendency to weaken the inferior recti and superior oblique muscles whichturn the eyes down, thus creating discomfort for the wearer in lookingfrom distance vision to reading vision, and which also has a tendency tocreate double vision. I am able to overcome these difficulties bygrinding the distance portion in the reading portion so that the segmentcomes in the upper portion of the lens with a fine hair line dividingthe distance and reading portions. By. making the bifocal lens in thismanner, there is no spherical aberration to cause discomfort to thewearer and the lens can be made of less weight than any other bifocal.lens with whichI am familiar.

The full objects and advantages of my invention will appear inconnection with the detailed description thereof, and the novel featuresembodied in my inventive idea will be particularly pointed out in theclaim. This application is a division of my prior application SerialNumber 380,729, filed May 12, 1920.

In the accompanying drawings,-

Fig. 1 is a plan view of a blank piece of optical glass. Fig. 2 is aview in central section through Fig. 1. Fig. 3 is a plan view showingthe blank of Fig. 1 with an additional piece of glass cemented thereto.Fig. 4 is a view in central section throu h Fig. 3.- Fig. 5 is a planview showing e combined structure of Figs. 3. and 4 after grinding. Fig.6 is a View in central section through Fig. 5. Fig. 7 is a plan view inwhich the product of Figs. 5 and 6 has been cut in half after removal ofthe additional piece of glass. Fig. 8 is a plan view of one of thehalves shown'in Fig; 7 after it has been ground on the convex side. Fig.9 is a view in section on the lines 9-9 of Fig. 8. Fig. 10 is a planview of the fin.- ished lens.

' In carrying out my invention, I start with a concave-convex blank 12of optical glass such as shown in Figs. 1 and 2. 'I grind the concaveside of this blank to the 7 curvature called for by the prescription forthe reading portion of the lens and thus produce the part-1y groundblank 14. I then grind the convex side of a concavo-convex piece ofglass 16 so that it will fit upon the concave side of the ground blank14 and secure the two pieces together as shown in Figs. 3 and 4,preferably by a cement that will stand heat or cold, so that the two,pieces will be held securely together. then grind a countersink throughthe piece 16 and into the concave face of the blank 14 in accordancewith the curvature called for by the distance portion of the lens, thusproducing the ground-out portion 18 in the blank 14 and reducing thepiece 16 to the annular form shown at 20 and producing the hair line ofseparation 22 between the distance portion and the reading portion. Thering 20 which has served as a guide during the grinding operation isthen detache and the partlyground blank is cut in two in well-knownmanner to produce the' two halves shownin Fig. 7. I then grind theconvex side of these two halves with the desired curvature as shown inFigs.

8 and 9, after which they are cut to the desired oval shape, asindicated on the dotted line 24 in Fig. 8, to produce the finishedarticle shown'in Fig. 10. The points 26 'the term .opticalfcenfefirefersto a difierent thin from the term geometrical center.

edge of the lens, while the optical center is the point of no prismaticefl'ect and is in the thinnest part of a concave lens andin.

the thickest part of a convex lens or plus lens.

The advantages of my invention will obvious from the foregoingdescription.

geometrical center of a lens is' that point in the lens which isequi-distant from all oppositely located points on the partly groundblank serves as a guide in grmding the distance portion of the lens inthe reading portion so that a. fine hairline of separation is veryaccurately positioned between the two portions of the lens. -It isobvious that my invention is particularly applica ble to toric lenses.

I claim: A one-piece bifocal minus eye-glass lens for myopic correctionshaving a lower readseparated from each other by a fine h'air line, bothof said portions having optical centers of their own located in thethinnest ing portion and an upper'drstance portion 50 points of saidportions, respectively; and

on opposite sides of said line.

1 In testimony whereof I hereunto siganture. f

WILLIAM F. FISHER.

